Hydraulic equipment raising and stresscontrol devices for farming tractors



March 7, 1967 L. PERAS 3,307,455

HYDRAULIC EQUIPMENT RAISING AND STRESS-CONTROL DEVICES FOR FARMINGTRACTORS Filed March- 2, 1964 3 Sheets-Sheet 1 Invenlor Lucien e -'65 8fm, MM W W/MM gifzowneyg.

March 7, 1967 PE 7 HYDRAULIC EQUIPMENT RAISING AND STRESS'CONTROLDEVICES FOR FARMING TRACTORS Filed March 2, 1964 5 Sheets-Sheet 2 Im/ehZw Lac fen pe ma 8 14 iorne y I r I March 7, 1967 L. PERAS 3,307,455

HYDRAULIC EQUIPMENT RAISING AND STRESS-CONTROL DEVICES FOR FARMINGTRAGTORS Filed March 2, 1964 3 Sheets-Sheet 5 D P 180 v 173 Imus/i140!Lucien aras United States Patent 3,307,455 HYDRAULIC EQUIPMENT RAISINGAND STRESS- CONTROL DEVICES FOR FARMING TRACTORS Lucien Peras,Billancourt, France, assignor to Regie Nationale des Usines Renault,Billancourt, France, a French works Filed Mar. 2, 1964, Ser. No. 348,540Claims priority, application France, Mar. 4, 1963, 926,788, Patent1,363,918; Sept. 16, 1963, 947,625, Patent 1,37 6,690

14 Claims. (Cl. 91-367) This invention relates to hydraulic devicesadapted to raise the equipment or tool carried by farming tractors, totransfer the equipment load to the tractor, and to control the tractiveeffort exerted on the equipment. It applies notably to tractors of thetype comprising a singleacting hydraulic equipment-raising cylindercontrolling one or a plurality of lifting arms having their endsconnected through links to the traction rods carrying the equipment,tool or implement of the tractor.

This invention relates more particularly to a device comprising incombination a preselector-type control in the form of a preselectorhandlever adjustable as a function of the desired vertical or depthposition of the equipment, and another control of the tractive-efforttype, i.e. responsive to the resistant stress produced by the equipmentduring the ploughing or other soil-working operation, this last-namedcontrol being adapted to limit this stress to a preselected value byacting upon the tool operation depth, that is, upon the raising deviceproper, so that the tractor will operate with a predetermined constantor maximum tractive effort.

It is an object of this invention to provide a specific form ofembodiment of a dual-control device of the type broadly set forthhereinabove, which is characterized by a greatly simplified constructionand by a considerable degree of manoeuverabiiity, the operator havingfurthermore the choice of using only one of the two control meansavailable in the device.

Generally, two solutions may be resorted to for controlling either thetractive eifort of the tractor vehicle or the resistant effort of theequipment during its operation:

(a) The first solution consists in creating in the equipment raisingcylinder pressure values determined beforehand as a function of the typeof work to be performed, these pressure values being obtained wheneverthe tractive effort rises to certain predetermined corresponding values;

This first solution requires a nearly constant throttling of thehydraulic fluid, as a rule oil, in an open-center hydraulic circuit,i.e. a circuit wherein a distributor having at least three ports or waysprovides a continuous fluid flow from the first port to the second and/or third ports.

(b) The second solution consists in causing automatically a slightupward movement of the equipment each time the resistant effortincreases by a predetermined value in order to decrease this resistanteffort and therefore reduce to zero the equipment-raising control actionin conjunction with the stabilization of the working depth of theequipment at a value consistent with or corresponding to a giventractive effort.

Conversely, when the tractive effort decreases, the effort detectingdevice will control automatically the means for lowering the equipmentin order to increase the working depth of the equipment until thepreselected tractive effort is restored.

This second solution is advantageous in that the feed pump operates onlyduring the equipment raising periods for altering the working depth,without requiring a constant throttling of the fluid.

In the device according to the present invention, which ice is based onthis second solution, the equipment raising cylinder is connected to adistributor comprising a slidevalve for controlling the delivery ofhydraulic fluid from a source of fluid under pressure such as a pumpeither to said raising cylinder through an inlet valve in a firstposition of the movable member of said slide valve or from saidequipment raising cylinder through an exhaust valve to an exhaust ductconnected to the reservoir feeding said source in the second position ofsaid slide valve in which the movable member of the slide valve is urgedby spring means, or directly to said exhaust valve in the intermediateposition of the aforesaid movable member of the slide valve. Moreover,this movable member of the slide valve may assume other intermediatepositions in which, instead of causing the complete closing or openingof the ports concerned, it produces a more or less pronounced throttlingthereof.

The desired position of the equipment raising arm is obtained by meansof a preselector control arrangement incorporating a preselectorhandlever and interconnected through suitable linkage means with thishandlever, the slide valve and the raising arm.

An effort control system co-operates with the slide valve and isconnected to the draw-gear or coupling system incorporating resilientmeans responsive to the tractive effort when the latter exceeds apredetermined value. This effort control system comprises a firstpivoting bearing member so arranged that the draw-gear may exerttherethrough a certain force on the slide valve in the direction of thefirst position thereof. The permissible movement of said bearing memberin the direction of this force is limited by an adjustable stop memberprovided on an adjustment handlever.

The linkage means comprise a second pivoting bearing member also adaptedto act upon the slide valve.

The operative connections between said first pivoting bearing member andthe draw-gear, on the one hand, the between said second pivoting bearingmember, said raising arm and said preselector handlever, on the otherhand, are so designed that a tractive effort exerted on the draw-gearwhich has a force sufficient to overcome the resistance of the resilientmeans, the movement of said preselector handle in one direction as Wellas the lowering of the raising arm, are capable of causing the slidevalve member to move in the direction of its first position. Conversely,if this tractive effort decreases to a value sulficient to render thetractive eifort exerted by said resilient means preponderant, adisplacement of the preselector handlever in the opposite direction, adisplacement of the adjustment handlever in the direction to enable itsstop member to exert a pressure against the first pivoting bearingmember and an upward movement of the raising arm, will cause .the slidevalve to move toward its second position.

This invention is also concerned with a distributor device of which theslide valve is responsive to the various mechanical control elements setforth hereinabove.

This distributor device comprises essentially inlet and exhaust valves,a cock adapted to connect the source of hydraulic fluid under pressuredirectly to the feed reservoir of said source, a controlled relief valveand a distributor proper.

The cock is controlled from a double-acting cylinder the inner space ofwhich is divided by its piston into a closing chamber containing aspring urging said piston in the cock closing direction and an openingchamber connected to said source of hydraulic fluid under pressure,whereby the application of this pressure in this opening chamber willdrive said piston in the cock opening direction.

Said relief valve comprises a piston-like shutter opening with one endinto a cavity into which a sliding valve seat is also adapted to open.This sliding seat communicates with the exhaust duct and is urged byspring means toward said shutter of which the other end opens into acontrol chamber adapted to be connected either to the source ofhydraulic fluid under pressure or to said discharge duct.

The distributor proper comprises around its slide valve member a firstchamber communicating with the source of hydraulic fluid under pressure,a second chamber communicating with the raising cylinder through saidinlet valve, with the closing chamber of said cock and with the cavityof said relief valve, and a third chamber communicating with saidcontrol chamber of said relief valve and with said discharge duct. Thesethree chambers disposed around the slide valve are separated from eachother by two partitions disposed the one between said first and secondchambers, and the other between said second and third chambers.

The slide valve incorporating said valve shutter disposed in said secondchamber is adapted to close an orifice formed through said firstpartition and is connected through an axial stem to a piston-typeshutter disposed at the level of saidthird chamber ar d adapted to closeeither a passage formed through said second partition or a passageleading to the discharge duct. The distance between the seat of thevalve shutter and the edge of the port into which said seat opens intosaid third chamber and the distance between the shutters are socalculated that in the first position the slide valve will free thepassage between said three chambers, that in the second position it willprevent the communication between these chambers and that in theintermediate position it will free only the passage between the firstchamber and the second chamber. The duct connecting the equipmentraising cylinder to the inlet valve communicates with the discharge ductthrough the medium of the exhaust valve the opening of which iscontrolled mechanically by the slide valve member when it is moved toits second position.

Two typical forms of embodiment of the hydraulic raising deviceaccording to this invention are described hereinafter by way of examplewith reference to the accompanying drawings. Other features andadvantages of the invention will appear as the description proceeds. Inthe drawings:

FIGURE 1 illustrates diagrammatically in section an equipment raisingmechanism constructed according to the teachings of this invention;

FIGURE 2 is a diagrammatic sectional view showing the rear portion of atractor of which the left-hand wheel has been removed, with the carriedequipment consisting in this case of a plough;

FIGURE 3 is a diagrammatic section showing on a larger scale a reliefvalve incorporated in the distributor device of this invention;

FIGURE 4 to 6 illustrate diagrammatically three different positions ofthe distributor slide valve;

FIGURE 7 is another diagrammatic sectional view showing an alternateform of embodiment of the equipment raising device of this invention;

FIGURE 8 illustrates diagrammatically a modified mounting of the raisingdevice of FIGURE 7, at the rear of a tractor; and I FIGURE 9 is a detailview showing an alternate form of embodiment of the distributor slidevalve.

The device of this invention is comprised of an assembly of mechanicalcomponent elements illustrated in the right-hand portion of FIGURES land 2, which assembly is adapted to act upon a single control member ofthe distributor shown in the left-hand portion of FIG- URE 1, thiscontrol member being sunk more or less in the distributor body duringthe operation of the assembly.

The traction rods 1 permitting the rigid mounting of a farming equipmentsuch as a plough are pivotally mounted by means of their pivot pins 2 onthe crank-pins 3 of a crankarm 4 adapted to rotate about a mainshaft 5mounted in the casing of the final drive of the tractor. The tractionrods 1 are suspended from a lifting link 6 pivoted on the end of alifting arm 7 rigid with a control lever 8 pivotally mounted on aspindle 9 also carried by said casing. An equipment raising cylinder 10of which the movable element or piston bears through the medium of athrust rod 11 against the end of one of the arms of said lever 8 exertson the lifting arm 7 and raising link 6 a stress counter-acting theforce tending to lower the equipment.

The c-rankarm 4 is rigid with another lever 12 of which the permissibleangular amplitude is limited by stop members 13 and 14. A tractionspring 15 constantly urges the lever 12 towards the stop 13, i.e. in adirection opposite to the direction in which this lever is urged by thetractive force exerted by the equipment.

A first bearing member 16 in the form of a bell-crank lever pivoted onthe end of lever 12 by mean-s of a pivot pin 17 and adapted to pivot inthe same directions as this lever, has its free end registering with thecontrol member or push-rod 18, another tension spring 19 urging thisfree end for engagement with the aforesaid push-rod, as shown. Thepermissible angular movements of this first bearing member 16 isrestricted, in the direction in which it is urged by the spring 19, dueto the provision of an adjustable stop 20, consisting for example of theloosed bottom of an axial blind bore of a tube 21 pivoted on a lever 22rigid with a control handlever 23 pivotally mounted on a fixed pivot pin24, this blind bore being engaged by a rod 25 pivotally mounted on saidfirst bearing member 16.

A cam 26 of which the operative contour registers likewise with saidpush-rod 18 is pivotally mounted on a fixed pivot pin 27. A first rod 28is pivoted at one end on a point of said cam which is spaced from itsaxis of rotation and at its other end on an intermediate point ofanother rod 29 also pivoted at one end on the arm of control lever 8which is opposite to that engaged by the thrust rod 11. The other end ofrod 29 is connected through a third pivoted rod 30 to one end of a lever31 rigid with a preselector control handlever 32 pivoted about a fixedpivot pin 33.

In order better to distinguish the movable pivot points from the fixedpivot points on the tractor or its final drive casing, these pins areshown in the form of shaded discs in FIGURE 2.

The form of embodiment of the distributor device according to thisinvention which is illustrated in FIGURES l and 3 to 6 consists of aunitary block in which are incorporated the inlet and exhaust valves 34and 35, respectively, the cock 36 adapted to connect the delivery duct37 of a pump 38 directly to the reservoir 39 filled with hydraulic fluidsuch as oil, the relief valve 40 and the distributor proper 41. Thisdistributor device communicates with the reservoir 39 through adischarge duct 42 and with the cylinder 10 through a pipe line 43.

The member controlled directly by the mechanical control membersillustrated in the right-hand side of FIG- URE 1 is the slide valvemember 44 constantly urged against the aforesaid push-rod 18 by a spring45.

The slide valve 44 is slidably mounted in the distributor 41 shown on alarger scale in FIGURE 4. This distributor comprises around its slidevalve member and from the end adjacent to push-rod 18 three chambers 46,47 and 48 in axial alignment. The first chamber 46 is separated from thesecond chamber 47 by a partition through which an orifice 49 is formed,and the second chamber 47 is separated from the third chamber 48 byanother partition in which a passage 50 is formed, this third chamber 48being separated in turn from a cavity 51 by'a partition formed'with apassage 52.

The slide valve member 44 is a one-piece member projecting from thedistributor 41 with a cylindrical end portion 53 engaged by the push-rod18. Any fluid leaking between this cylindrical end portion 53 and thesurrounding bore in the distributor wall is collected by a cavity 54communicating through a passage 55 with the discharge duct 42.

As seen from its cylindrical end 53 the slide valve member 44 comprisesa frustoconical valve portion 56 disposed in the second chamber 47 andadapted to close the orifice 49, a piston-type shutter 57 disposed inthe plane of the third chamber 48 and adapted to close either passage 50or passage 52, and finally a cam portion 58 disposed in the cavity 51and adapted to hold the shutter 59 of exhaust valve 35 open or unseatedby means of a ball 60 and a control rod 61. A passage 62 formed in theslide valve body connects the cavity 51 to the discharge duct 42. Thedistances between the valve shutter 56, piston shutter 57 and cam 58, onthe one hand, and between the seat of valve shutter 56 in orifice 49,the edges by which passage 50 and cavity 51 open into the third chamber48 and the ball 60, on the other hand are so calculated that thecommunication between the first, second and third chambers isestablished, that between the third chamber 48 and cavity 51 isdiscontinued and exhaust valve 35 is closed when the slide valve memberhas completed its stroke to the -left, as shown in FIG- URE 4, and thatthe slide valve member closes the passage between the chambers, freesthe passage between the third chamber 48 and cavity 51 and the dischargeduct 42, and causes the opening of the exhaust valve 35 when it attainsits endmost position to the right (FIG- URE 6). In an intermediateposition (see FIGURE 5) the slide valve member frees only the passagefrom the first chamber to the second chamber. Of course, the slide valvemember may occupy intermediate positions in which the different passagesare more or less throttled.

The cock 36 comprises a cylindrical chamber 63 connected to the deliveryduct 37, and through a duct 64 to the first chamber 46 of distributor 41and through a passage 65 do the discharge duct 42. Slidably fitted inthe cylindrical chamber 63 is a first piston 66 which carries, alignedon one side and in this order, a valve shutter 67 and another, smallerpiston 68 sliding in a closed cylinder 69. A duct 70 formed in the valveshutter 67 and the second piston 68 maintains a permanent communicationbetween the delivery duct 37 and the space formed between the secondpiston 68 and the bottom of the closed cylinder 69. On the other side ofsaid first piston 66 a spring 71 housed in a closed chamber 72 exerts aresilient force on the first piston 66 so that the valve shutter beurged against the seat-forming passage 65. The closed chamber 72communicates with the second chamber 47 of distributor 41.

The relief valve 40 of which one portion is illustrated on a largerscale in FIGURE 3 comprises a piston-type 1 shutter 73 sliding in acylinder 74. This shutter 73 opens with one of its ends into a cavity 75communicating with the closed chamber 72 of cock 36, a sliding seat 76opening likewise into this chamber, as shown. This sliding seatcommunicates with the discharge duct 42 and is urged by a spring 77 inthe direction of shutter 73. How ever, its stroke is limited in thisdirection by a shoulder 78. The other end of shutter 73 opens into acontrol chamber 79 communicating with the aforesaid third chamber 48 ofdistributor 41. The diameter 80 of said sliding seat 76 engageable bysaid shutter is smaller than either the diameter 81 of cylinder 74 orthe diameter 82 of the passage in which the seat 76 is slidably fitted(see FIGURE 3).

Finally, the pipe line 43 connected to the raising cylinder communicateson the one hand with the second chamber 47 of distributor 41 through themedium of the inlet valve 34 permitting the flow of hydraulic fluid fromthis chamber to the cylinder and on the other hand with the dischargeduct 42 through the intermediary of the aforesaid exhaust valve 35.Throttling devices such as an adjustable needle valve 83 interposed inthe duct 64 connecting the cylindrical chamber 63 of cock 36 to thefirst chamber 46 of distributor 41 and another adjustable needle valve84 mounted immediately upstream of the exhaust valve 35 permit a properlimitation of the equipment raising and lowering speeds.

A throttling device 85 may also be provided in the duct connecting theclosed chamber 72 of cook 36 to the second chamber 47 of thedistributor, the function of this device being explained presently.

Finally, another cook 86, for example a three-way cock, which may beinterposed in the pipe line 43 connecting the raising cylinder 10 to thedistributor device permits of closing this line and to connect otherapparatus operated by the hydraulic fluid under pressure than theraising cylinder 10 to the distributor device.

The equipment-raising device described hereinabove by way of exampleoperates as follows:

(1) Efiort control device.-The tractive effort exerted in the linkage inthe direction of the arrow shown on the traction rod 1 of FIGURE 1varies as a function of the type of work to be performed by theequipment and varies also during the Work performed by a given equipmentas a function of the changes arising inevitably in the nature of thesoil as the tractor and equipment unit is operated.

As long as the tractive effort remains below a predetermined value thespring 15 holds the arm 12 stationary against the stop 13. When thiseffort rises above this value the arm 12 moves to the left and elongatesthe spring 15 until the spring force balances the tractive effortthrough the medium of the arms of lever 12 and crankshaft 4.

Thus, for each value of the tractive effort which lies within theadjustment range contemplated by construction, the lever 12 will occupya position between stop 13 and stop 14.

During its movements this lever 12, through the intermediary of pivotpin 17, carries along the first bearing member 16. Thus, this bearingmember 16 is caused to occupy different positions as a function of thevariations in the tractive effort and therefore, as a function of thesepositions, to engage the push-rod 18 and to move same more or less tothe left.

Moreover, it is possible to vary the position of the first bearingmember 16 in relation to this lever 12 by means of the handle 23, lever22, stop 20 and rod 25.

As a result, different positions of push-rod 18 can be obtained for asame position of lever 12, thus permitting the proper adjustment ofpresetting of the beginning of the upward pulse given to theequipment-raising means in relation to the value of the tractive effort.

Thus, with the first bearing member 16 adjusted for maximum sensitivity,it will contact the push-rod 18 and cause the hydraulic fluid pressurein the equipmentraising cylinder to increase when the lever 12 ceasesfrom hearing against the stop member 13. On the other hand, if the firstbearing member 16 is adjusted for minimum sensitivity corresponding tothe higher range of tractive efforts it will be necessary that lever 12attains a position relatively remote from stop member 13 (whichcorresponds to a substantial value of the tractive effort) before thefirst bearing member 16 causes a pressure increase by depressing thepush-rod 18.

When the first bearing member 16 is in its endmost position to the left(FIGURE 4) abutting against the push-rod 18 and while lever 12 continuesits leftward movement, the first bearing member 16 tilts due to thesliding movement of rod 25 in its tube 21 and thereby causes elongationof spring 19.

(2.) Equipment raising controL-The second bearing member, that is, cam26, acts upon the push-rod 18 in conjunction with, but independentlyfrom, the first bearing member 16.

Starting from the neutral Position of the slide 44 when the lever 32 ismoved towards the right in the drawing, the link 30 is pulled towardsthe left by the small lever 31 rigidly connected with the lever 32. Thelink 29 turns around its pivot point on the lever 8 in clockwisedirection and forces the link (28) to move towards the left andtherefore to turn the cam 26 in counter-clockwise direction. This causesthe displacement of the slide 44 towards the left and the feeding of thejack.

The feeding of the jack causes the lever 8 to turn around the pin 9 andthe lever 32 being then fixed, this has the effect of returning the link28 to the right, carrying along the cam 26 in clockwise direction. Themovement stops when the slide 44 has returned, under the action of thespring 45, into neutral position.

For control of descent, the procedure is the same but the lever 32 is inthis case moved towards the left.

(3) Conjugate action of the equipment-raising control and of the stresscontrol means.-When cam 26 is in its neutral position, the first bearingmember 16 cannot act upon push-rod 18 save for moving same to the leftto its initial neutral position, that is, only for controlling apressure increase and therefore an upward movement of the equipment.

When the first bearing member 16 moves to the right from the neutralposition of push-rod 18, the latter remains in engagement with cam 26and therefore no control of a downward movement below the positionpreselected by means of the preselector control handlever 32 can takeplace.

With this arrangement it is possible to combine the positionpreselection with the stress control, whereby the maximum working depthof the equipment is determined in an unchanging manner by thepreselection, and the stress control is effective for producing a loadtransfer followed by a gradual upward movement of the equipmentimmediately when the tractive effort equals or exceeds a predeterminedvalue.

When it is desired that the position of the equipment be determined onlyby the effort control device, the position preselector control handlever32 must be so placed that cam 26 be positioned somewhat backwards inrelation to the neutral position of push-rod 18.

From the intermediate position of slide valve 44 in which the raisingarm 7 is kept in a predetermined position the distributor device permitsof controlling either the upward movement of the equipment by moving theslide valve to the left, or the downward movement of the equipment bymoving said slide valve to the right.

In the intermediate or neutral position of slide valve 44 (see FIGUREthe hydraulic fluid is allowed to flow from the first chamber 46 to thesecond chamber 47, and from the third chamber 48 to the exhaust duct 42through cavity 51 and passages 62. Since the control chamber 79 ofrelief valve 40 is connected to the discharge duct 42 through the thirdchamber 48, the fluid delivered by pump 38 and flowing freely into thecavity 75 of relief valve 40 through the circuit comprising the deliveryduct 37, cylindrical chamber 63 of valve 36, duct 64, first and secondchambers 46, 47 and throttling device 85, unseats the shutter 73 due tothe pressure exerted on the relevant annular portion corresponding tothe difference between diameters 80 and 81 (see FIGURE 3). Therefore,this hydraulic fluid may flow freely through the sliding seat 76 to thedischarge duct 42 without exerting any control pressure in the closingchamber 72 of valve 36. Under these conditions, the oil deliverypressure prevailing in the cylindrical chamber 63 of valve 36 acts uponthe first piston 66 and through duct 70 upon the second piston 68thereof, these pistons compressing the coil spring 71 and unseating theshutter 67 to free the passage 65 through which the major portion of theoil is returned directly to the reservoir 39 through the discharge duct42. The throttling device 85 assists in conjunction with the adjustableneedle valve 83 in establishing in the cylindrical chamber 63 of valve36 the fluid pressure necessary for opening this valve.

The upward movement of the equipment (see FIG- URE 4) is controlled bymoving the slide valve 44 left wards; it has been explained hereinabovethat this movement could be caused either by the cam 26 or by the firstbearing member 16 transmitting the reactions of the equipment during thework.

During its movement the slide valve 44 frees the passage betWeenchambers 46, 47 and 48, while closing the passage 52 between the thirdchamber 48 and cavity 51. The moderate oil pressure prevailing in thiscase in the second chamber 47 is transmitted to control chamber 79 ofrelief valve 40 wherein it applies the shutter 73 against its slidingseat 76.

As the return of oil to the reservoir 39 through the sliding seat 76 isdiscontinued the pressure becomes substantially equal to that prevailingin the closing chamber 72 and in the cylindrical chamber 63 of valve 36;in other words, this pressure becomes equal on either side of pistons 66and 68. Therefore, spring 71 will seat the valve shutter 67.

Since the fluid cannot flow freely through the passage 65 and since thesliding seat 76 of relief valve 40 is fully closed, this fluid is forcedinto the raising cylinder by flowing along duct 64, first and secondchambers 46, 47 around the unseated ball 34 of the inlet valve, andfinally through the pipe line 43.

It will be noted that the quantity of oil discharged through passage 65is determined by the pressure differential obtaining between thecylindrical chamber 63 and the closing chamber 72, irrespective of thevalue of the pressures prevailing in these chambers. Now this pressuredifferential varies as a function of the throttling actions produced inthe circuit downstream of valve 36. The throttling action produced bythe adjustable needlevalve 83 may be adjusted permanently with a view toreduce under all circumstances the maximum feed rate of the cylinder,the throttling action of orifice 49 which is caused by the valve shutter56 varying on the other hand as a function of each slide valve movement.Thus, it will be seen that when a relatively short slide valve movementtakes place as the orific 49 is throttled considerably the fluid outputto the cyinder will be very small, whereas a longer slide valve strokewill practically elimimate the throttling action so that the feed rateof the cylinder can attain its maximum value determined by theadjustment of needle valve 83.

The throttling device 85 is designed to permit a rapid pressure drop inclosing chamber 72 when shutter 73 begins to move away from its slidingseat 76 in order to ensure a clean return of valve shutter 67 of valve36 to its open position.

The downward movement of the equipment (see FIG- URE 6) is controlled bya movement of slide valve 44 to the right.

When the cam 26 is moved away from the distributor body the coil spring45 moves the slide valve member 44 to the right, thus holding it incontact with the cam. As it completes its stroke (i.e. after having cutoff the passage between the three chamber 46, 47 and 48) the slide valvemember 44 unseats by means of its cam 58 the ball 60 which unseats inturn the shutter 59 of exhaust valve 35 through the medium of thecontrol push-rod 61. This shutter 59 is hydraulically balanced andseated only by the spring 86 (FIGURE 1). The oil contained in thecylinder is thus discharged to the reservoir through pipe line 43,needle valve 84 and discharge duct 42.

Finally, one of the component elements of the distributor device, therelief valve 40, is also adapted to operate as a pressure limitingdevice. The shutter 73 of this valve comprises a stop member limitingits stroke in the direction of its sliding seat 76.

When the shutter 73 under the influence of the pressure build up-inchamber 79 is abutting it also bears against its sliding seat 76 whichhas moved and partially compressed spring 77 (see FIGURE 3). If thepressure in cavity 75, (which applies to the annular section of slidingseat 76 corresponding to the difference existing between the diameter 82of the bore in which said seat is slidably mounted and the diameter 80engaged by the shutter on this seat) exceeds the value corresponding tothe calibration of spring 77, the sliding seat 76 by compressing to agreater extent the spring 77 will move away from shutter 73 and open thepassage leading to discharge duct 42. Under these conditions, thepressure decreases immediately in the closing chamber 72 of valve 36,due to the throttling device 85 limiting the permissible re-feeding ofsaid closing chamber, thus opening valve 36 and discharging the oilthrough passage 65 to the discharge duct 42.

A modified form of embodiment of the raising device of this inventionwill now be described with reference to FIGURES 7 and 9.

In this alternate form of embodiment the preselector handlever isprovided with a stop member co-acting unidirectionally with the secondbearing member pivoting in the direction permitting the positivedisplacement of this member and of the slide valve for producing theequipment raising movement. slide valve in the opposite direction tendsto keep the second bearing member in contact with said stop member. Thepivoted linkage of the preselector control system comprises an elementco-acting undirectionally with the raising arm provided with a stopmember, said element being urged by said spring for engagement with thisstop member. The stop member of the adjustment handlever is so disposedthereon that it acts as a counter-stop to said first pivoting bearingmember in order to adjust according to its position the setting intooperation of the slide valve in the equipment raising direction when thetractive effort exceeds a predetermined value.

As shown in FIGURE 8 the tractor 101 of this modified arrangementcomprises a three-point equipment coupling system comprising as inconventional systems of this character two lateral traction rods 102pivoted on the rear part of the tractor frame and raising links 103connected on the other hand on the end of a raising arm 104 pivoted onthe tractor frame structure by means of a pivot pin 105.

The equipment illustrated in this case is also a plough pivotallyconnected to the rods 102 at 106 and to another link 107 at a thirdpoint 108.

As shown in FIGURE 7, co-a-cting with the raising arm 104 is asingle-acting cylinder 109 having its cylinder body 110 rigid with thetractor and its piston 111 connected through a thrust rod 112 to theaforesaid arm 104.

Connected through a pipe line 113 is a hydraulic device 114 fordistributing fluid under pressure from the reservoir 115 through themedium of a pump 116 and a delivery duct 117, a discharge duct 118connecting the distributor device 114 to the reservoir 115, as shown.

This distributor device comprises a slide valve member 119 slidablyfitted in the distributor body forming a plurality of spaced annularchambers adapted to be isolated from one another by means of slide-valveshutters, notably chambers 120, 121 separable by a valve shutter 122 andchamber 123 separable from chamber 121 by means of a piston shutter 124.

The pump delivery duct 117 is connected to a duct 125 of the distributordevice which communicates permanently with the aforesaid chamber 120,this duct 125 having inserted therein a valve 126 having its valveshutter adapted to engage a seat 127 to control the fluid flow toanother duct 128 connected to the discharge duct 118. The valve shutterof valve 126 is in the form of a sliding piston having a closing controlchamber 129 containing a coil spring 130 and connected to the aforesaidchamber 121 by means of a duct 131 in which a relief valve or pilotvalve 132 of valve 126 is inserted. This valve 132 is The spring urgingthe' also of the sliding piston type formed at one end with a shutteradapted to engage a seat 133 through which the duct 131 communicateswith another duct 134 constantly connected to the discharge duct 128.

At the other end of valve 132 a control chamber 135 constantly connectedto chamber 123 is provided.

Chamber 121 is connected through an inlet valve 136 to a duct 137communicating normally through a cock 138 with a duct 139 leading to theaforesaid pipe line 113. This duct 139 is also constantly communicatingwith a duct 140 in which a needle valve 141 is inserted, this duct 140having in addition with a duct 142 connected to the discharge duct 128 acommunication controlled by an exhaust valve 143 of the balanced typewhich is urged to its seated position by a spring 144. This valve 143 iscontrolled by means of a ball 145 engaged by a cam face or ramp 146 (seeFIGURE 9) formed on the sliding member 119 cf the distributor slidevalve.

On the other hand a safety valve 150 is connected to the control chamber129 of valve 126. This safety valve 150 consists of a piston-like memberslidably mounted in a bore 151 and carrying a shutter 152 adapted toengage a seat 153 opening int-o the chamber 129. This shutter 152 formswith the valve bore and the piston an annular chamber 154 constantlycommunicating with a duct 155 which a rotary cock 156 is adapted toeither isolate from, or connect through its inner passages 157 with, aduct 158 connected in turn to the discharge duct 142. On the sideopposite to the shutter 152 the valve 150 is urged by a spring 159housed in a chamber 160 having a diameter somewhat greater than that ofbore 151, and the piston sliding in this bore is formed with at leastone flat side face 161 forming in the bore 151 a passage permitting thecommunication between the annular chamber 154 and the chamber 160 aftera certain compression of spring 159 which corresponds to a backwardmovement of shutter 152, said chamber 160 communicating permanently withthe duct 158 through a duct 161 and the passage of cock 156.

The slide valve member 119 of the distributor has one end urged againsta control push-rod 162 by one end of a compression spring 163 bearingagainst the distributor body with its other end.

At the ends of the slide valve member a pair of chambers 164 and 165 areprovided which communicate respectively with the discharge ducts 142 and128, chamber 164 communicating in addition through a passage 166 formedin slide valve member 119 with an annular space 167 formed between thismember 119 and the surrounding cavity, this passage 166 being adapted tocommunicate or not with chamber 123 according to the position of thepiston shutter 124 of the slide valve in relation to the slide valvemember 119.

In this form of embodiment the push-rod 162 is springloaded and consistsof'two members 162 162 slidably mounted in each other with a spring 168interposed therebetween, their relative expansion being limited by a pin169. Spring 168 is tightened with a force greater than that of spring163 in its maximum compressed position, whereby the push-rod 162 actsnorm-ally as a rigid memher with respect to spring 163. This push-rod162 carries a pin 170 on which are pivoted intermediate their ends thesecond pivoting bearing member and the first pivoting bearing member, inthe form of a lever 172, of a tractive effort control system.

The second pivoting bearing member 171 is an integral part of a linkageinterposed between an adjustable preselector handlever 173 and theraising arm 104. The preselector handlever 173 is provided with a stop174 co-acting unidirectionally with one end of the other bearing member171 having its opposite end connected to a link 175 pivoted on the otherhand intermediate the ends of lever 176, this lever 176 having one endpivoted on a fixed pin 177 of the tractor and the other end coactingunidirectionally with a stop member 178 carried by said raising arm 104.This linkage is so designed that the aforesaid spring 163 of slide valve119 constantly urges through push-rod 162 the second bearing member 171and lever 176 in contact with stop members 174 and 178.

The first bearing member 172 is an integral part of a linkage interposedbetween an effort-control adjustment lever 180 and the equipmentcoupling system comprising resilient means responsive to the tractiveeffort, which means in this example consists of a compression spring181. This spring 181 is interposed between the tractor frame structureand a guide push-member 182 responsive to the action of a lever 183forming an integral part of a crankshaft pivoted on a fixed pivot pin184 and provided, on the other hand, with crankpins 185 on which theaforesaid traction rods 102 are pivoted as at 186. Lever 183 bearsagainst the tractor frame structure as illustrated in FIGURE 7 for agiven degree of prestress of spring 181 which is determined as afunction of the range of tractive efforts to which the spring isrequired to react by deformation.

The adjustment lever 180 is formed with a stop member 187 adapted toengage unidirectionally one end of the first pivoting bearing member 172of which the other end is connected to a link 188 which, by means of abell-crank lever 189 pivoted on pin 177, co-acts with another link 190connected in turn to the lever 183 of said crankshaft.

The control handlevers 173 and 180 are mounted on a common fixed pin 191and can be locked in relation thereto in any desired angular position bymeans of any known and convenient device designed for control means ofthis character, this locking system being no part of the presentinvention.

It will be seen firstly that the preselector control system implies thatto each selected angular position of the preselector handlever 173 therecorresponds a predetermined angular position of the equipment raisingarm 104 in which as both elements 171 and 176 bear against stop elements174 and 178, the distributor slide valve member 119 is in itsintermediate or neutral position which is the position shown in FIGURE7.

In this position, the oil delivered by pump 116 into the delivery duct125 is returned to the reservoir through thevalv'e 126, the shutter ofthis valve being unseated by the fact that the oil delivery pressureexceeds the force of spring 130since no pressure exists in the closingchamber 129; stress may be laid on the fact that in spite of a possibleflow of fluid from chamber 120 to chamber 121 in the neutral position ofthe slide valve the duct 131 is then connected to the reservoir throughthe seat of pilot valve element 132 of valve 126.

To produce the upward movement of arm 104 and therefore of the equipmentcarried thereby, the operator moves the preselector handlever 173 in thedirection of the arrow M. In this case the push-rod 162 moves the slidevalve member 119 to the left, thus disposing the valve shutter 122 andpiston shutter 124 of the slide valve in such positions that the annularchambers 120, 121 and 123 communicate with one another, chamber 123being isolated from the reservoir 115. As a result, the shutter memberof pilot valve 132 is responsive to a preponderant pressure in controlchamber 135 which urges said member to its closed position against seat133, this pressure preponderance being due notably to the presence of athrottled passage 192 formed in the duct 131 and to the preliminaryopening of the seat 133 of this valve.

Under these conditions the pressure built up in the closing chamber 129of valve 126 attains a value tending to equal the oil delivery pressuretoward the reservoir through this valve, whereby the shutter thereofwill then be urged to its closed position by the spring 130. Under theseconditions the oil pressure rises in the circuit involved and thecylinder 109 is then fed through the inlet valve 136. This produces anupward movement of arm 104 and therefore of the equipment,simultaneously with a movement to the right (as seen in the drawing) ofthe stop member 178, so that the linkage 176, 175, 171, push-rod 162 andslide valve member 119 move back to the right as seen in the drawinguntil they are stopped in a stable position when the slide valve member119 has resumed its neutral position.

In fact, it will be noted that as slide valve member 119 resumes itsneutral position the piston shutter 124 thereof simultaneously separateschambers 121 and 123 from each other and restores the communicationbetween this chamber 123 and control chamber 135, on the one hand, andreservoir 115, on the other hand, thus causing the opening of seat 133of pilot valve 132 and a pressure drop in closing chamber 129 of valve126, whereby the oil pressure exerted against this valve 126 becomesagain preponderant in relation to the action of spring and causes theopening of seat 127 to restore the communication between the pump andthe reservoir. During this return movement of the slide valve member toits intermediate or neutral position the throttled passage 192 permits arapid pressure drop in closing chamber 129 immediately as the seat 133is re-opened, thus causing a clean return of valve shutter 126 to itsopen position.

To obtain a downward movement of arm 104 the preselector handlever 173must be moved in the direction of the arrow D. In this case the spring163 urges the slide valve member 119 and push-rod 162 to the right, asseen in the figures, together with the second pivoting bearing member171 due to the clearing of stop member 174 in relation thereto, and inaddition the movement of slide valve member 119, while maintaining thecircuit in the by-pass condition, will open by means of the cam face orramp 146 the exhaust valve 143 to vent the cylinder 109. This venting ofcylinder 109 takes place through needle valve 141, whereby the rate ofdownward movement of the equipment can be adjusted at will. Thisinvolves a downward movement, toward the left-hand side of the figures,of stop member 178, whereby the linkage system comprising 176, 175, 171,pushrod 162 and slide valve 119 resumes a stable position correspondingto the intermediate or neutral position of slide valve member 119 inwhich position this member 119 permits the re-closing of exhaust valve143.

If it is required to raise the equipment, the preselector controlhandlever 173 may be moved in the direction M 1n such a manner that itinvolves a movement of pin of slide valve member 119 which is greaterthan the permissible stroke of this member 119 toward the left-hand sideof the figures, for when the slide valve member abuts in the distributorbody while compressing home the spring 163, the spring-loaded member 162retracts to permit a complementary movement of pin 170.

Of course the push-rod 162 could also consist of a rigid member but inthis case the operation, in the case of raising movements of relativelygreat amplitude, should accompany the preselector handlever 173 to thedesired position as the equipment is actually raised.

It will be noted that the interaction between this preselector controland the effort control means produces through the pivot pin 170 adisplacement of the first pivoting bearing member 172 of this last-namedcontrol means of which the movement takes place with-out anyinterference whatsoever in case of equipment raising movement and mustbe assured, to permit the above-described operation in case of downwardmovement, by the provision of a minimum play e between the stop member187 of adjustment handlever 180 and the element 172 of the effortcontrol, this play e being such as to permit the movement of pin 170 tothe extent necessary for actuating the exhaust valve 143.

The above-described tractive effort control device operates as follows:

The effort required for pulling the equipment or tool during the work(for example the ploughing of a soil), which corresponds to theresistant effort exerted in the direction of the arrow F on the tractionrods 102, varies as a function of the type of work performed and duringa same type of work according to changes intervening in the quality ofthe soil.

As long as this effort F transmitted to the spring 181 in the mannerdescribed hereinabove exerts on this spring a force inferior to theprestress force of said spring, the

lever 183 remains in abutment against the frame structure of the tractorand the effort control system is inoperative in relation to thepreselector control by which the desired working depth of the equipmentwas preset.

When this effort F increases until the spring 181 is compressed to acondition of equilibrium depending on the effort involved, the lever 183is raised and through the elements 190, 189 and 188 the first pivotingbearing member 172 is caused to move angularly about the pivot pin 170directed toward the abutment 187 of adjustment handlever 180.

From the moment the first pivoting bearing member 172 engages the stopmember 187, the movement of this member 172. is changed to a pivotingmovement, during which said stop'member 187 serves as a fulcrum, thuscausing the translation of pivot pin 170 of push-rod 162 to the left, asseen in the figures, and moving consequently the slide valve member 119in the direction to release the hydraulic feed of cylinder 109 and causethe upward movement of the tractor equipment under the conditions'already set forth. The thus initiated raising movement of the equipmentcauses the effort F exerted on the tracti-on rods 102 to decrease,whereby the spring 181 is somewhat allowed to expand. When as aconsequence of the foregoing the linkage 183, 190, 189, 188 and 172resumes its preceding position in which the first bearing member 172engaged the stop member 187, the pivot pin 170 has resumed the positioncorresponding to the neutral position of slide valve member 119 in whichthe distributor is again in its by-pass condition, as already explained.Thus, the overstepping of a predetermined tractive effort involvedautomatically the application of a raising impulse to the equipmentwhich tends to regularize the necessary tractor hauling effort.

It may also be noted that when the slide valve member 119-has resumedits neutral position, with the first pivoting bearing member 172engaging the stop member 187 under the conditions set forth hereinabove,the linkage system of the preselector control assembly has a certainplay in relation to the stop members 174, 178 due to theequipment-raising impulse which has just been controlled by the effortcontrol system.

If in this case the tractive effort dropped below the value havingcaused the first bearing member 172 to contact stop member 187, spring181 will expand further and slide valve member 119 will then be causedto move to the right, as seen in the figures, in the direction tooperate the exhaust valve 143 of the cylinder, as permitted by theaforementioned play stored by the preselector control. Under theseconditions, the equipment will be lowered to a greater working depth,thus tending to compensate the aforesaid reduction in tractive effortand therefore to regularize this reduction.

It will be noted that if under these conditions the tractive effortcontinues to decrease, the downward movement of the equipment can belimited when the aforementioned play given to the preselector controlhas been taken up, for this control will then become operative to returnthe slide valve and the control elements associated therewith to theirinitial neutral positions shown in the drawing.

It is clear that this dual-control device permits of combining thepreselector control means with the effort control means, so that themaximum working depth of the equipment be determined by the preselectorcontrol means whereas the effort control means are effective to limitthe tractive effort to a predetermined maximum value.

Of course, the maximum working depth may be selected by means of thepreselector control and set to such a value that the effort controlbecomes preponderant during the operation, if desired.

More particularly, it will be noted that the tractive effort value abovewhich the effort control becomes operative is simply determined by theposition of stop member 187 and therefore of the adjustment handlever180 located within easy reach of the operator. The displacement of theadjustment handlever 180 in the direction P (FIG- URE 7) will causenotably the compression stroke of spring 181 to increase, thusincrementing the effort value at which the effort control becomesoperative, whereby this adjustment handlever 180 enables the operator toselect the desired sensitivity of the effort control as a function ofthe type of work to be or being performed.

On the other hand, any overload in the feed circuit of cylinder 109 issafety avoided due to the provision of the safety or relief valve in thedistributor body, this valve co-acting with the valve 126 under thefollowing conditions:

When the control lever ofcock 156 is so positioned that chamber 154 ofvalve 150 is connected through a passage thereof with the discharge duct142, the maximum value of the circuit pressure is that above which theshutter 152 is lifted off its seat 153, thus connecting the closingchamber 129 of valve 126 to the exhaust and causing the immediateopening of the seat 127 of this valve so as to connect the pump with thereservoir.

' latter compresses the spring 159 until the fiat face 161 of thepiston, by receding, opens the communication between chambers 154 and160. As this last-named chamber 160 is constantly communicating with thereservoir, as already explained the closing chamber 129 of valve 126 isexhausted, whereby the maximum pressure is limited by the opening ofthis valve. In this case the safety pressure may be selected to have alower value than in the preceding case, the use of two safety pressurevalues depending if desired on specific working conditions, and maynotably be useful in case the distributor were used for feeding loadother or auxiliary apparatus outside the equipment raising cylinder 109,which are adapted to be connected to the distributor through the duct139 and fed by means of the three-way cock 138 so as to isolate theraising cylinder 109 in this case.

Although the present invention has been described notably in conjunctionwith two preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope type, comprising a single-acting raising cylinderco-acting with at least one equipment lifting arm, an equipment couplingsystem to which said lifting arm is connected and comprising tractionlinks, a source of hydraulic fluid under pressure, a hydraulicdistributor device comprising a movable slide valve member fordistributing the hydraulic fluid delivered from said source of fluidunder pressure either, in a first position of said slide valve member,to said raising cylinder through an inlet valve, or, in a secondposition of said slide valve member toward which said valve member isurged by a spring, from said raising cylinder through an exhaust valveto a discharge duct connected to the reservoir feeding said source, or,furthermore, in an intermediate position of said slide valve member,directly to said discharge duct, it being understood that otherintermediate positions and actions of said slide valve member arepermitted, a preselector control comprising a handlever for preselectingthe desired position of said lifting arm and a linkage systeminterconnecting said preselector handlever, said slide valve member andsaid lifting arm, an effort control system co-acting with said slidevalve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effort control system comprising a firstpivoting bearing member a-buttingly engaged with said slide valve memberand so designed and mounted that said coupling system is capable,through the medium of said bearing member, of exerting a certain forceon said slide valve member in the direction of said first positionthereof and of which the permissible movement in the direction of saidlast-named force is limited by an adjustable stop provided on anadjustment handlever, said linkage system comprising a second pivotingbearing member abuttingly engaged with said slide valve member and alsoadapted to act upon said slide valve member while the connectionsbetween said first pivoting bearing member and said coupling system, onthe one hand, and between said second pivoting bearing member, saidlifting arm and said preselector handlever, on the other hand, are sodesigned and arranged that atractive effort exerted on said couplingsystem and of a value sufficient to overcome the force of said resilientmeans, the displacement of said preselector handlever in one directionas well as the lowering of said lifting arm be capable of causing thedisplacement of said slide valve member in the direction of said firstposition, and that a reduction in the tractive effort which causes theeffort exerted by said resilient means to become preponderant as well asa displacement of said preselector handlever in the opposite direction,a displacement of said adjustment handlever in the direction to enableits adjustable stop to exert a pressure on the first pivoting bearingmember and an upward movement of said lifting arm be capable of causingthe displacement of said slide valve member in the direction of saidsecond position.

2. Hydraulic equipment raising device as set forth in claim 1,characterized in that said second bearing member consists of a cam.

3. Hydraulic equipment raising device as set forth in claim 1,characterized in that said pivoting bearing members act upon said slidevalve member through the medium of a push-rod guided in the body of saiddistributor device.

4. Hydraulic equipment-raising and tractive-effort control device forfarming tractors of the carried equipment type, comprising a singleacting raising cylinder coacting with at least one equipment liftingarm, an equipment coupling system to which said lifting arm is connectedand comprising traction links, a source of hydraulic fluid underpressure, a hydraulic distributor device comprising a movable slidevalve member for distributing the hydraulic fluid delivered from saidsource of fluid under pressure either, in a first position of said slidevalve member, to said raising cylinder through an inlet valve, or, in asecond position of said slide valve member toward 15 which said valvemember is urged by a spring, from said raising cylinder through anexhaust valve to a discharge duct connected to the'reservoir feedingsaid source, or, furthermore, in an intermediate position of said'slidevalve member, directly to said discharge duct, it being understood thatother intermediate positions and actions of said slide valve member arepermitted, a preselector control comprising a handlever for preselectingthe desired position of said lifting arm and a linkage systeminterconnecting said preselector handlever, said slide valve member andsaid lifting arm, an effort. control system coacting with said slidevalve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effortcontrol system comprising a firstpivoting bearing member so designed and mounted that said couplingsystem is capable, through the medium of said bearing member, ofexerting a certain force of said slide valve member in the direction ofsaid first position thereof and of which the permissible movement in thedirection of said last named force is limited by an adjustable stopprovided on an adjustment handlever, said linkage system comprising asecond pivoting bearing member also adapted to act upon said-slide valvemember while the connections between said first pivoting bearing memberand said coupling system, on the one hand, and between said secondpivoting bearing member, said lifting arm and said preselectorhandlever, on the other hand, are so designed and arranged that atractive effort exerted on said coupling system and of a valuesufficient to overcome the force of said resilient means, thedisplacement of said preselector handlever in one direction as well asthe lowering of said lifting arm be capable of causing the displacementof said slide valve member in the direction of said first position, andthat a reduction in the tractive effort which causes the effort exertedby said resilient means to become preponderant as well as a displacementof said preselector handlever in the opposite direction, a displacementof said adjustment handlever in the direction to enable its adjustablestop to exert a pressure on the first pivoting bearing member and anupward movement of said lifting arm be capable of causing thedisplacement of said slide valve member in the direction of said secondposition, characterizedin that said first bearing member is a leverhaving one end so disposed as to be capable of exerting upon one of theends of said slide valve member an effort in the axial direction of saidslide valve member, the other end of said lever being subjected to theaction ofa spring so that said first end may exert a force upon saidslide valve member in the direction of said first position of said slidevalve member.

5. Hydraulic equipment raising device as set forth in claim 4,characterized in that said second bearing member consists of a cam.

6. Hydraulic equipment raising device as set forth in claim 5,characterized in that the movable member of said hydraulic cylinderbears against one arm of a control lever solid with the lifting arm,said coupling system comprising a first link having one end pivoted onsaid second bearing member and the other end pivoted on one point ofanother link pivoted in turn'by means of a third link on a lever armrigid with said preselector control handlever.

7. Hydraulic equipment raising device as set forth in claim 4,characterized in that the movable member of said hydraulic cylinderbears against one arm of'a control lever solid with the lifting arm,said coupling system comprising a first link having one end pivoted onsaid second bearing member and the other end pivoted on one point ofanother link pivoted in turn by means of a third link on a lever armrigid with said preselector control handlever.

8. Hydraulic equipment-raising and tractive-effort control device forfarming tractors of the carried equipment type, comprising a singleacting raising cylinder coacting with a least one equipment lifting arm,an equipment coupling system to which said lifting arm is connected andcomprising traction links, a source of hydraulic fluid under pressure, ahydraulic distributor device comprising a movable slide valve member fordistributing the hydraulic fluid delivered from said source of fluidunder pressure either, in a first position of said slide valve member,to said raising cylinder through an inlet valve, or, in a secondposition of said slide valve member toward which said valve member isurged by a spring, from said raising cylinder through an exhaust valveto a discharge duct connected to the reservoir feeding said source, or,furthermore, in an intermediate position of said slide valve member,directly to said discharge duct, it being understood that otherintermediate positions and actions of said slide valve member arepermitted, a preselector control comprising a handlever for preselectingthe desired position of said lifting arm and a linkage systeminterconnecting said preselector handlever, said slide valve member andsaid lifting arm, an effort control system coacting with said slidevalve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effort control system comprising a firstpivoting bearing member so designed and mounted that said couplingsystem is capable, through the medium of said bearing member, ofexerting a certain force on said slide valve member in the direction ofsaid first position thereof and of which the permissible movement in thedirection of said last named force is limited by an adjustable stopprovided on an adjustment handlever, said linkage system comprising asecond pivoting bearing member also adapted to act 'upon said slidevalve member while the connections between said first pivoting bearingmember and said coupling system, on the one hand, and between saidsecond pivoting bearing member, said lifting arm and said preselectorhandlever, on the other hand, are so designed and arranged that atractive effort exerted on said coupling system and of a valuesuflicient to overcome the force of said resilient means, thedisplacement of said preselector handlever in one direction as well asthe lowering of said lifting arm be capable of causing the displacementof said slide valve member in the direction of said first position, andthat a reduction in the tractive effort which causes the effort exertedby said resilient means to become preponderant as well as a displacementof said preselector handlever in the opposite direction, a displacementof said adjustment handlever in the direction to enable its adjustablestop to exert a pressure on the first pivoting bearing member and anupward movement of said lifting arm be capable of caus ing thedisplacement of said slide valve member in the direction of said secondposition, characterized in that the movable member of said hydrauliccylinder bears against one arm of a control lever solid with the liftingarm, said coupling system comprising a first link having one end pivotedon said second bearing member and the other end pivoted on one point ofanother link pivoted in turn by means of a third link on a lever armrigid with said preselector control handlever.

9. Hydraulic equipment-raising and tractive-effort control device forfarming tractors of the carried equipment type, comprising a singleacting raising cylinder coating with at least one equipment lifting arm,an equipment coupling system to which said lifting arm is connected andcomprising traction links, a source of hydraulic fluid under pressure, ahydraulic distributor device comprising a movable slide valve member fordistributing the hydraulic fluid delivered from said source of fluidunder pressure either, in a first position of said slide valve member,to said raising cylinder through an inlet valve, or, in a secondposition of said slide valve member toward which said valve member isurged by a spring, from said raising cylinder through an exhaust valveto a discharge duct connected to the reservoir feeding said source, or,furthermore, in an intermediate position of said slide valve member,directly to said discharge duct, it being understood that otherintermediate positions and actions of said slide valve member arepermitted, a preselector control comprising a handlever for preselectingthe desired position of said lifting arm and a linkage systeminterconnecting said preselector handlever, said slide valve member andsaid lifting arm, an effort control sys tem co-acting with said slidevalve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effort control system comprising a firstpivoting bearing member so designed and mounted that said couplingsystem is capable, through the medium of said bearing member, ofexerting a certain force on said slide valve member in the direction ofsaid first position thereof and of which the permissible movement in thedirection of said last named force is limited by an adjustable stopprovided on an adjustment handlever, said linkage system comprising asecond pivoting bearing member also adapted to act upon said slide valvemember while the connections between said first pivoting bearing memberand said coupling system, on the one hand, and between said secondpivoting bearing member, said lifting arm and said preselectorhandlever, on the other hand, are so designed and arranged that atractive effort exerted on said coupling system and of a valuesufiicient to overcome the force of said resilient means, thedisplacement of said preselector handlever in one direction as well asthe lowering of said lifting arm be capable of causing the displacementof said slide valve member in the direction of said first position, andthat a reduction in the tractive effort which causes the effort exertedby said resilient means to become preponderant as well as a displacementof said preselector handlever in the opposite direction, a displacementof said adjustment handlever in the direction to enable its adjustablestop to exert a pressure on the first pivoting bearing member and anupward movement of said lifting arm be capable of causing thedisplacement of said slide valve member in the direction of said secondposition, said second bearing member consisting of a 'cam, characterizedin that the movable member of said hydraulic cylinder bears against onearm of a control lever solid with the lifting arm, said coupling systemcomprising a first link having one end pivoted on said second bearingmember and the other end pivoted on one point of another link pivoted inturn by means of a third link on a lever armrigid with said preselectorcontrol handlever.

10. Hydraulic equipment-raising and tractive-effort control device forfarming tractors of the carried equipment type, comprising a singleacting raising cylinder coacting with at least one equipment liftingarm, an equipment coupling system to which said lifting arm is connectedand comprising traction links, a source of hydraulic fluid underpressure, a hydraulicdistributor device comprising a movable slide valvemember for distributing the hydraulic fluid delivered from said sourceof fluid under pressure either, in a first position of said slide valvemember, to said raising cylinder through an inlet valve, or, in a secondposition of said slide valve member toward which said valve member isurged by a spring, from said raising cylinder through an exhaust valveto a discharge duct connected to the reservoir feeding said source, or,furthermore, in an intermediate position of said slide valve member,directly to said discharge duct, it being understood that otherintermediate positions and actions of said slide valve member arepermitted, a preselector control comprising a handlever for preselectingthe desired position of said lifting arm and a linkage systeminterconnecting said preselector handlever, said slide valve member andsaid lifting arm, an effort control system coacting with said slidevalve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effort control system comprising a firstpivoting bearing member so designed and mounted that said couplingsystem is capable, through the medium of said bearing member, ofexerting a certain force on said slide valve member in the direction ofsaid first position thereof and of which the permissible movement in thedirection of said last named force is limited by an adjustable stopprovided on an adjustment handlever, said linkage system comprising asecond pivoting bearing member also adapted to act upon said slide valvemember while the connections between said first pivoting bearing memberand said coupling system, on the one hand, and between said secondpivoting bearing member, said lifting arm and said preselectorhandlever, on the other hand, are so designed and arranged that atractive effort exerted on said coupling system and of a valuesufficient to overcome the force of said resilient means, thedisplacement of said preselector handlever in one direction as well asthe lowering of said lifting arm be capable of causing the displacementof said slide valve member in the direction of said first position, andthat a reduction in the tractive effort which causes the effort exertedby said resilient means to become preponderant as well as a displacementof said preselector handlever in the opposite direction, a displacementof said adjustment handlever in the direction to enable its adjustablestop to exert a pressure on the first pivoting bearing member and anupward movement of said lifting arm be capable of causing thedisplacement of said slide valve member in the direction of said secondposition, characterized in that said first pivoting bearing member andsaid second pivoting bearing member are pivoted at their fulcrums on acommon pivot pin controlling the displacement of said slide valve memberof said distributor device, said preselector handlever being providedwith stop means co-acting unidirectionally with said second pivotingbearing member in the direction to permit the positive displacement ofsaid second pivoting bearing member and said slide valve member toobtain a lifting, said spring which urges said slide valve member in theopposite direction tending to keep said second pivoting bearing memberin contact with said stop member, said linkage system of saidpreselector control comprising a member co-acting unidirectionally withsaid lifting arm formed with a stop against which said last-named memberis urged by said spring, said stop member of said adjustment handleverbeing so disposed thereon that it acts as a counterbearing stop means tosaid first pivoting bearing member in order to adjust as a function ofits position the operation of said slide valve member in theequipment-raising direction from a predetermined value of the tractiveeffort transmitted from the equipment.

11. Hydraulic equipment-raising device as set forth in claim 10,characterized in that said movable member of said hydraulic cylinderbears against one of the arms of a control lever solid with said liftingarm, the member which co-acts unidirectionally with said lifting armconsisting of an inter-resistant lever or a lever of the second order ofwhich the free end is caused to engage said stop member disposed on saidother arm of said control lever, while said second pivoting bearingmember consists of a lever having on one side of its fulcrum an arm keptin contact with said stop member of said preselector handlever and onthe other side of said fulcrum another arm connected through a link tothe point of application of the resistant effort of said inter-resistantlever or lever of the second order.

12. Hydraulic equipment raising device as set forth in claim 10,characterized in that said distributor device comprises the followingcomponent element: a valve adapted to connect said source of hydraulicfluid under pressure directly to said reservoir feeding said source,said valve being controlled by a double-acting cylinder having its innerspace divided by a piston into a closing chamber containing acompression spring urging said piston in the direction to close saidvalve, and an opening chamber connected to said source of hydraulicfluid under pressure and in which the fluid pressure urges said pistonin the valve opening direction, a controlled relief valve of which apiston-forming shutter opens with one end into a cavity into which openslikewise a valve seat communicating with the discharge duct and with theopposite end into a control chamber, a distributor comprising about saidslide valve member a first chamber communicating with said source ofhydraulic fluid under pressure, a second chamber communicating with saidequipment raising cylinder through the medium of said inlet valve, withsaid closing chamber of said valve and with the cavity of said reliefvalve, a third chamber communicating with said control chamber and withsaid discharge duct, said first, second and third chambers beingseparated by a first partition disposed between said first and secondchambers and by a second partition disposed between said second andthird chambers, said slide valve member comprising a valve-type shutterdisposed in said second chamber and adapted to close an orifice formedin said first partition and connected through an axial rod to apistontype shutter disposed at the level of said third chamber andadapted to close either a passage formed in said second partition oranother passage leading to said discharge duct, the space left betweenthe seat of said valve-shutter and the edge of said passage leading intosaid third chamber, on the one hand, and the distance between saidshutters, on the other hand, being such that in its first position saidslide valve member frees the passage between said three chambers andthat in its second position it prevents the communication between saidchambers and that in the intermediate position it frees only the passagebetween said first chamber to said second chamber while the ductconnecting said equipment raising cylinder to said inlet valvecommunicates with said discharge duct through said exhaust valve theopening of which is controlled mechanically by said slide valve memberwhen the latter is moved to its second position.

13-. Hydraulic equipment-raising device as set forth in claim 12,wherein devices for reducing the cross-sectional area are provided inthe duct connecting said second chamber to said cavity of said reliefvalve, in the duct connecting said raising cylinder to said exhaustvalve, and possibly in the duct connecting said first chamber to saidsource of fluid under pressure.

14. Hydraulic equipment-raising and tractive-effort control device forfarming tractors of the carried equipment type, comprising a singleacting raising cylinder coacting with at least one equipment liftingarm, an equipment coupling system to which said lifting arm is connectedand comprising traction links, a source of hydraulic fluid underpressure, a hydraulic distributor device comprising a movable slidevalve member for distributing the hydraulic fluid delivered from saidsource of fluid under pressure either, in a first position of said slidevalve member, to said raising cylinder through an inlet valve, or, in asecond position of said slide valve member toward which said valvemember is urged by a spring, from said raising cylinder through anexhaust valve to a discharge duct connected to the reservoir feedingsaid source, or, furthermore, in an intermediate position of said slidevalve member, directly to said discharge duct, it being understood thatother intermediate positions and actions of said slide valve member areper mitted, a preselector control comprising a handlever forpreselecting the desired position of said lifting arm and a linkagesystem interconnecting said preselector handlever, said slide valvemember and said lifting arm, an effort control system coacting with saidslide valve member and connected to said coupling system incorporatingresilient means responsive to the tractive effort above a predeterminedvalue of said effort, said effort control system comprising a firstpivoting bearing member so designed and mounted that said couplingsystem is capable, through the medium of said bearing member, ofexerting a certain force on said slide valve member in the direction ofsaid first position thereof and of which the permissible movement in thedirection of said last named force is limited by an adjustable stopprovided on an adjustment handlever, said linkage system comprising asecond pivoting bearing member also adapted to act upon said slide valvemember while the connections between said first pivoting bearing memberand said coupling system, on the one hand, and between said secondpivoting bearing member, said lifting arm and said preselectorhandlever, on the other hand, are so designed and arranged that atractive effort exerted on said coupling system and of a valuesufficient to overcome the force of said resilient means, thedisplacement of said preselector handlever in one direction as well asthe lowering of said lifting arm be capable of causing the displacementof said slide valve member in the direction of said first position, andthat a reduction in the tractive effort 20 enable its adjustable stop toexert a pressure on the first pivoting bearing member and an upwardmovement of said lifting arm be capable of causing the displacement ofsaid slide valve member in the direction of said second position,characterized in that said coupling system is adapted to exert a forceon said slide valve member through a traction rod pivoted on a crankpinof a crankshaft movable about an axis fixed on said tractor, saidcrankshaft being solid with a one-arm lever retained by a spring actingagainst the force to which it is subjected by the equipment during thework, said one-arm lever being connected through said effort controlsystem to said first bearing member.

References Cited by the Examiner UNITED STATES PATENTS 7/1951 Newgen91-367 2/1961 Hershman 91-367

1. HYDRAULIC EQUIPMENT-RAISING AND TRACTIVE-EFFECT CONTROL DEVICE FORFARMING TRACTORS OF THE CARRIED EQUIPMENT TYPE, COMPRISING ASINGLE-ACTING RAISING CYLINDER CO-ACTING WITH AT LEAST ONE EQUIPMENTLIFTING ARM, AN EQUIPMENT COUPLING SYSTEM TO WHICH SAID LIFTING ARM ISCONNECTED AND COMPRISING TRACTION LINKS, A SOURCE OF HYDRAULIC FLUIDUNDER PRESSURE, A HYDRAULIC DISTRIBUTOR DEVICE COMPRISING A MOVABLESLIDE VALVE MEMBER FOR DISTRIBUTING THE HYDRAULIC FLUID DELIVERED FROMSAID SOURCE OF FLUID UNDER PRESSURE EITHER, IN A FIRST POSITION OF SAIDSLIDE VALVE MEMBER, TO SAID RAISING CYLINDER THROUGH AN INLET VALVE, OR,IN A SECOND POSITION OF SAID SLIDE VALVE MEMBER TOWARD WHICH SAID VALVEMEMBER IS URGED BY A SPRING, FROM SAID RAISING CYLINDER THROUGH ANEXHAUST VALVE TO A DISCHARGE DUCT CONNECTED TO THE RESERVOIR FEEDINGSAID SOURCE, OR, FURTHERMORE, IN AN INTERMEDIATE POSITION OF SAID SLIDEVALVE MEMBER, DIRECTLY TO SAID DISCHARGE DUCT, IT BEING UNDERSTOOD THATOTHER INTERMEDIATE POSITIONS AND ACTIONS OF SAID SLIDE VALVE MEMBER AREPERMITTED, A PRESELECTOR CONTROL COMPRISING A HANDLEVER FOR PRESELECTINGTHE DESIRED POSITION OF SAID LIFTING ARM AND A LINKAGE SYSTEMINTERCONNECTING SAID PRESELECTOR HANDLEVER, SAID SLIDE VALVE MEMBER ANDSAID LIFTING ARM, AN EFFORT CONTROL SYSTEM CO-ACTING WITH SAID SLIDEVALVE MEMBER AND CONNECTED TO SAID COUPLING SYSTEM INCORPORATINGRESILIENT MEANS RESPONSIVE TO THE TRACTIVE EFFORT ABOVE A PREDETERMINEDVALUE OF SAID EFFORT, SAID EFFORT CONTROL SYSTEM COMPRISING A FIRSTPIVOTING BEARING MEMBER ABUTTINGLY ENGAGED WITH SAID SLIDE VALVE MEMBERAND SO DESIGNED AND MOUNTED THAT SAID COUPLING SYSTEM IS CAPABLE,THROUGH THE MEDIUM OF SAID BEARING MEMBER, OF EXERTING A CERTAIN FORCEON SAID SLIDE VALVE MEMBER IN THE DIRECTION OF SAID FIRST POSITIONTHEREOF AND OF WHICH THE PERMISSIBLE MOVEMENT IN THE DIRECTION OF SAIDLAST-NAMED FORCE IS LIMITED BY AN ADJUSTABLE STOP PROVIDED ON ANADJUSTMENT HANDLEVER, SAID LINKAGE SYSTEM COMPRISING A SECOND PIVOTINGBEARING MEMBER ABUTTINGLY ENGAGED WITH SAID SLIDE VALVE MEMBER AND ALSOADAPTED TO ACT UPON SAID SLIDE VALVE MEMBER WHILE THE CONNECTIONSBETWEEN SAID FIRST PIVOTING BEARING MEMBER AND SAID COUPLING SYSTEM, ONTHE ONE HAND, AND BETWEEN SAID SECOND PIVOTING BEARING MEMBER, SAIDLIFTING ARM AND SAID PRESELECTOR HANDLEVER, ON THE OTHER HAND, ARE SODESIGNED AND ARRANGED THAT A TRACTIVE EFFORT EXERTED ON SAID COUPLINGSYSTEM AND OF A VALUE SUFFICIENT TO OVERCOME THE FORCE OF SAID RESILIENTMEANS, THE DISPLACEMENT OF SAID PRESELECTOR HANDLEVER IN ONE DIRECTIONAS WELL AS THE LOWERING OF SAID LIFTING ARM BE CAPABLE OF CAUSING THEDISPLACEMENT OF SAID SLIDE VALVE MEMBER IN THE DIRECTION OF SAID FIRSTPOSITION, AND THAT A REDUCTION IN THE TRACTIVE EFFORT WHICH CAUSES THEEFFORT EXERTED BY SAID RESILIENT MEANS TO BECOME PREPONDERANT AS WELL ASA DISPLACEMENT OF SAID PRESELECTOR HANDLEVER IN THE OPPOSITE DIRECTION,A DISPLACEMENT OF SAID ADJUSTMENT HANDLEVER IN THE DIRECTION TO ENABLEITS ADJUSTABLE STOP TO EXERT A PRESSURE ON THE FIRST PIVOTING BEARINGMEMBER AND AN UPWARD MOVEMENT OF SAID LIFTING ARM BE CAPABLE OF CAUSINGTHE DISPLACEMENT OF SAID SLIDE VALVE MEMBER IN THE DIRECTION OF SAIDSECOND POSITION.